The present invention relates to fuel injectors for delivery of fuel to the intake system of an internal combustion engine and, more particularly, to an electromagnetic fuel injector that includes a dampening device applied to a moveable valve assembly. Most particularly, the present invention relates to an electromagnetic fuel injector dampening device that includes a internal adjustment for setting valve assembly stroke.
It is most desirable, in a modern internal combustion engine, to precisely control the flow of fuel to the combustion chamber, in order to meet performance requirements, as well as emission regulations. Various types of electromagnetic fuel injectors, which precisely control the flow of fuel through a valve seat, have been used for this purpose. Generally, an electromagnetic fuel injector incorporates a solenoid armature, located between the pole piece of the solenoid and a fixed valve seatxe2x80x94the armature operates as a moveable valve assembly.
Electromagnetic fuel injectors are linear devices that meter fuel per electrical pulse at a rate proportional to the width of the electrical pulse. The specific relationship between pulse width and fuel delivered or metered through the injector is dependent on the injector""s static flow, which typically is controlled by the stroke of the armature or moveable valve assembly of the injector, and its dynamic flow, which typically is a function of the closing force exerted on the moveable valve assembly by a spring load. U.S. Pat. No. 5,312,050, the disclosure of which is incorporated herein by reference, describes a fuel injector that engages an armature return spring and a center pole piece to vary, respectively, the dynamic and static flow characteristics of the fuel injector.
When an injector is energized, its moveable valve assembly is released from one stop position and accelerated by a spring towards the opposite stop position, located at the valve seat, the distance between the stop positions constituting the xe2x80x9cstroke.xe2x80x9d As applied to fuel injectors, the term xe2x80x9cbouncexe2x80x9d refers to the condition where the moveable valve assembly inside the injector xe2x80x9cbouncesxe2x80x9d off the valve seat one or more times after initial impact. Bounce at the valve seat is generally undesirable because it can cause unwanted fuel injection, which, because there is insufficient time for the excess fuel to be burned, has a deleterious effect on emissions.
Direct injection of gasoline, where the injector is positioned to inject fuel directly into the combustion chamber, requires a relatively high fuel pressure to operate. For example, a direct injection gasoline injector requires a pressure as high as 1700 psi or higher to operate while a typical port fuel injector requires a pressure of only approximately 60 psi to operate. The higher pressure of the direct injection gasoline injector requires the exertion of higher magnetic and spring forces on the valve assembly to operate properly. In turn, the higher the final velocity, the greater the mass of the moveable valve assembly, and the stiffer the valve assembly is at impact, the more likely is the occurrence of bounce.
The stroke through which the moveable valve assembly operates also effects the likelihood of bouncexe2x80x94the greater the stroke, the more likely bounce will occur. The accuracy at which the pole piece and the fixed valve seat can be positioned relative to each other and the consistency at which the valve assembly stroke can be set is therefore important.
Thus, there is a need for a fuel injector in which the movement of the valve assembly is dampened to reduce bounce. There is also a need in the art for a fuel injector wherein the stroke of the moveable valve assembly can be precisely and repeatedly controlled. These needs are met by the present invention.
The present invention, in one form thereof, is directed to a fuel injector having a body with a fuel inlet and a fuel outlet and a base. The base, which is sealably connected to the body, includes a valve seat. A moveable valve assembly having an armature and a valve outlet member is disposed at the fuel outlet for controlling the flow of fuel from the outlet. Positioned between the armature and valve outlet member is a dampening device that acts on the moveable valve assembly to reduce bounce of the valve outlet member at the valve seat.
Further in accordance with the present invention is an electromagnetic fuel injector having a body with a fuel inlet and a fuel outlet and a base. The base, which is sealably connected to the body, includes a valve seat. A moveable valve assembly having an armature and valve outlet member includes a pintle and a ball element that is disposed at the fuel outlet to control the flow of fuel from the outlet. At least one spring, positioned between the armature and the valve outlet member, acts on the moveable valve assembly to reduce bounce of the valve outlet member at the valve seat. The present invention also includes a means for adjusting the internal stroke of the injector after the injector is assembled.